This invention relates generally to overmoded waveguides and more particularly to a multiport rectangular TE.sub.10 to circular TE.sub.01 mode transducer.
Waveguides can generally be classified as "fundamental mode" or "overmoded". A fundamental mode waveguide is designed with dimensions which support only the fundamental electromagnetic field, or mode, configuration for propagation in a given frequency band. An overmoded waveguide is designed so that several or many modes can be supported with internal structures to suppress all but the desired modal configuration. In practice, the fundamental mode waveguide, also known as the "standard" waveguide, is far more common as it is more easily designed and constructed. However, the standard waveguide is severely restricted in maximum power capacity and in minimum loss because of its required cross sectional dimensions. The advantages of an overmoded waveguide are that it can be designed to have arbitrarily high power capacity and arbitrarily low attenuation by appropriately increasing the cross section. Required suppression of unwanted modes is achieved using dielectric and metallic structures to restrict allowable modes, see "Trunk Waveguide Communication," A. E. Karbowiak, Chapman and Hall, LTD, London, 1965.
Overmoded waveguides have been utilized as telecommunications trunk transmission lines and to connect transmitters to communications or radar antennas, see "WT4 Millimeter Waveguide System: Introduction," W. D. Waters, Bell System Technical Journal, Vol. 56, No. 10, Dec. 1977, pp. 1825-1827 and "Practical Aspects of High Power Circular Waveguide Systems," R. M. Collins, NEREM Record 1962, pp. 182-183. The most common type of overmoded waveguide supports the circular TE.sub.01 mode which has the unique property of decreasing transmission loss with increasing frequency for a given diameter, see "Trunk Waveguide Communication," A. E. Karbowiak, Chapman and Hall, LTD, London, 1965. Although applied most often to exploit the low-loss characteristic, the potential for overmoded waveguides to support higher power than standard waveguides has also been considered, see "On the Feasibility of Power Transmission Using Microwave Energy in Circular Waveguide," W. Lowenstein, Jr. and D. A. Dunn, The Journal of Microwave Power Symposium Proceedings, Part B, Vol. 1, No. 2, 1966, pp. 57-61.
Energy is generally supplied to or extracted from the desired mode in an overmoded waveguide from or by a standard waveguide via a "mode transducer". Several such mode transducers efficiently couple microwave or millimeter wavelength energy between a standard rectangular cross section waveguide TE.sub.10 mode and the overmoded circular cross section waveguide TE.sub.01 mode. One type of transducer involves direct transition from one mode to another through a region of gradually varying waveguide cross section. U.S. Pat. Nos. 2,859,412 to Marie, 2,779,923 to Purcell and 3,349,346 to Enderly teach this type of transducer which is generally efficient over a relatively wide frequency band.
Another type of rectangular TE.sub.10 to circular TE.sub.01 mode transducer is formed by providing a common wall between the rectangular and circular waveguides with modal coupling provided through holes or slots of specific separation in the common wall. Such transducers, including those taught in U.S. Pat. Nos. 2,848,690 to Miller, 3,918,010 to Marchalot and 3,369,197 to Giger, et al. provide efficient energy transfer over a more restricted bandwidth than the first type of transducer because of the particular spacing of the holes or slots relative to a guide wavelength. This bandwidth restriction can be alleviated by using special structures within the transducer, as taught by U.S. Pat. No. 2,948,864 to Miller.
Since the peak power carrying capacity of standard waveguides is generally lower than that of overmoded waveguides, the above transducers do not allow transfer of power to or from the overmoded waveguides at a level which the overmoded components are capable of supporting without substantial pressurization and cooling of the standard waveguide sections. Pressurization and temperature control are conventional methods of increasing standard waveguide power capacity, however, there are practical constraints to these methods.
The present invention teaches a device to appropriately connect multiple standard waveguides to an overmoded waveguide to increase transducer power capacity via division of power among the standard components. The U.S. Pat. No. 3,369,197 to Giger et al. teaches multiple waveguide feeds which are designed to couple to different overmoded waveguide modes or to different frequency channels but not to transfer maximum power. The present invention couples part of the geometry from the Marie transducer, U.S. Pat. No. 2,859,412 to a new section to provide a new transducer which divides power in the overmoded TE.sub.01 mode equally among several standard rectangular waveguides consistent with the standard waveguide's power capacities. This allows efficient coupling over a relatively wide bandwidth between the circular TE.sub.01 mode overmoded waveguide and a multiple of standard rectangular TE.sub.10 mode waveguides without requiring pressurization. The power capacity of the transducer taught by the present invention can be increased by simply increasing the diameter of the overmoded waveguide and increasing the number of standard rectangular waveguides feeding the transducer.
It is therefore one object of this invention to provide a multiport rectangular TE.sub.10 to circular TE.sub.01 mode transducer.
It is another object of this invention to provide a multiport rectangular TE.sub.10 to circular TE.sub.01 mode transducer for overmoded waveguides.
It is a further object of this invention to provide a multiport rectangular TE.sub.10 to circular TE.sub.01 mode transducer for overmoded waveguides that is capable of handling high power.
It is still another object of this invention to provide a multiport rectangular TE.sub.10 to circular TE.sub.01 mode transducer for overmoded waveguides that is capable of handling high power without requiring pressurization or cooling.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.